1. Field of the Invention
The present invention relates to an optical transceiver. more particularly, the invention relates to an optical transceiver having a transmitter section and a receiver section formed on a substrate to be close to each other, which suppresses the electrical and optical crosstalk between the transmitter section and the receiver section.
2. Description of the Related Art
FIG. 1 schematically shows the configuration of a prior-art optical transceiver of this type.
As shown in FIG. 1, the transceiver comprises a substrate 105, a transmitter section and a receiver section mounted on the surface of the substrate 105, and a ferrule 114 fixed at the front end of the substrate 105.
A semiconductor light-emitting element 101 (e.g., laser diode) for the transmitter section and a semiconductor light-receiving element 102 (e.g., photodiode) for the receiver section are mounted on the surface of the substrate 105. A metallic shielding plate 107 is fixed on the surface of the substrate 105 between the transmitter and receiver sections, thereby separating these two sections from each other. The plate 107 is perpendicular to the surface of the substrate 105.
At the front end of the substrate 105, the ferrule 114 is fixed for optical coupling of the transceiver with optical fibers. The ferrule 114 is formed by a synthetic resin processed precisely. Two optical fiber pieces 115 for optical interconnection are buried in the ferrule 114 to extend in parallel to each other from the front end of the ferrule 114 to the rear end thereof. The ferrule 114 is positioned with respect to the elements 101 and 102 on the substrate 105 with high accuracy. Thus, the light-emitting element 101 and the light-receiving element 102 on the substrate 104 are precisely positioned with respect to the corresponding fiber pieces 115 in the ferrule 114.
The ferrule 114 has two positioning protrusions 114a formed on its front end face to protrude forward.
When the prior-art transceiver of FIG. 1 is used, this transceiver is connected to an optical connector 110 supporting two optical fibers 111 by way of the ferrule 114. The connector 110 has two engaging holes 110a at its rear end face. The protrusions 114a of the ferrule 114 are opposed to these holes 110a. When the connector 110 is coupled with the transceiver, the protrusions 114a are inserted into and engaged with the corresponding holes 110a, resulting in the connector 110 and the ferrule 114 being coupled each other. Thus, accurate positioning between the ferrule 114 (i.e., the fiber pieces 115) and the connector 110 (i.e., the fibers 111) can be realized automatically.
The reference numerals 123 and 124 denote a transmitting LSI (Large-Scale Integrated circuit device) and a receiving LSI mounted on the surface of the substrate 105, respectively. The semiconductor light-emitting element 101 and the transmitting LSI 123 constitute the transmitter section. The semiconductor light-receiving element 102 and the receiving LSI 124 constitute the receiver section. The reference numeral 126 denotes wiring lines for electrical signals formed on the surface of the substrate 105.
With the prior-art optical transceiver shown in FIG. 1, it is one of the important requirements for improving the reception sensitivity to suppress the electrical and optical crosstalk between the transmitter and receiver sections on the substrate 105 without degrading the optical coupling efficiency of the fibers 111 with the light-emitting and light-receiving elements 101 and 102. To meet this requirement, the shielding plate 107 made of metal (e.g., Cu or Fe) is fixed on the surface of the substrate 105 between the transmitter and receiver sections.
Thus, electromagnetic waves generated in the transmitter section are prevented from affecting directly the receiver section. At the same time as this, stray light generated from the light emitted by the light-emitting element 101 is prevented from reaching the receiver section. The stray light is typically generated by the fact that small part of the light from the element 101 does not enter the corresponding optical fiber 111 by way of the corresponding optical fiber piece 115 and reflected in the vicinity of the element 101 and piece 115.
Moreover, the ferrule 114 is usually made of synthetic resin having a light-shielding property, where the resin contains an additive (e.g., a black pigment) with a light-absorbing property. The fiber pieces 115 buried in the ferrule 114 are used to block stray light traveling in the light-emission direction of the element 101. The rear end face of the ferrule 114 is formed in such a way that the light does not enter the inside of the ferrule 114 except for the rear ends of the fiber pieces 115.
An optical transceiver of this type, which comprises a transmitter section and a receiver section mounted on a substrate, is disclosed in, for example, the digest C-3-140 of the 2000 electronics society conference held by the Electronic Information and Communication Society.
However, the above-described prior-art optical transceiver with reference to FIG. 1 has the following problems.
Specifically, with the prior-art transceiver of FIG. 1, the ferrule 114 having the buried optical fiber pieces 115 is made of a synthetic resin and therefore, the front ends of the transmitter and receiver sections are covered with the resin-made ferrule 114. Thus, an electromagnetic wave propagating route 116 is formed near the front ends of these two sections, as shown in FIG. 1. This means that the effect of the electromagnetic wave that propagates along the route 116 from the transmitter section to the receiver section is unable to be blocked.
The material of the ferrule 114 can be changed from the resin to a metal having an effect of shielding the electromagnetic wave without changing the configuration of the prior-art transceiver of FIG. 1. In this case, however, another problem will occur. That is to say, the two penetrating holes for burying the fiber pieces 115 need to be formed in the metallic ferrule 114 at a specific interval in such a way as to be slightly larger than the diameter of the pieces 115 to be buried therein with extreme precision. However, such a precise hole-formation processing to a metal piece is very difficult to be realized. Furthermore, the obtainable productivity for this hole-formation processing will be low and thus, it will not be acceptable.
Moreover, the ferrule 114 may be formed by a synthetic resin having a property of absorbing electromagnetic waves. In this case also, however, another problem will occur. Generally, in substances having a property of absorbing electromagnetic waves, the effect of absorbing electromagnetic waves tends to deteriorate as the frequency of the electromagnetic wave is raised, if the frequency of the electromagnetic wave is several gigahertz (GHz) or higher. Therefore, if the transceiver operates at a high speed of 10 gigabits per second (Gb/sec) or greater, the obtainable effect of shielding electromagnetic waves will be low.
Needless to say, a metallic member may be additionally provided between the ferrule 114 and the substrate 105. In this case, however, there arises the need to place a gap for inserting the metallic member between the read ends of the fiber pieces 115 in the ferrule 114 and the light-emitting and light-receiving elements 101 and 102 on the substrate 105. This means that the optical coupling loss of the element 101 with the corresponding fiber piece 115 will increase.